1. Field of the Invention
The present invention relates to a communication device and a method used in a wireless communication system, and more particularly, to a communication device and a method of reporting channel information according to beamforming in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes at least one evolved Node-B (eNB) for communicating with at least one user equipment (UE), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, increases peak data rate and throughput, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (COMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), licensed-assisted access (LAA) using LTE, etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
In addition, beamforming is proposed to further improve the performance of the wireless communication system. In this situation the UE may receive a large amount of reference signals transmitted by the eNB according to the beamforming. Accordingly, the UE needs to report a large amount of channel information to the eNB by using the reference signals. The performance improvement provided by the beamforming is degraded due to overhead caused by the reporting of the channel information.
Thus, how to report the channel information according to the beamforming is realized is an important problem to be solved.